1. Field of the Invention
The present invention relates generally to fuel systems for internal combustion engines and more particularly to a method and apparatus for supplying a vaporized fuel to an internal combustion engine.
2. Description of the Prior Art
Fuel vapor systems which supply fuel vapor to an internal combustion engine are old in the art. Such systems are generally more fuel efficient than conventional liquid fuel systems because they deliver more spaced and uniformly spread fuel molecules to the combustion chamber, thereby promoting a shorter, more complete and hence, more efficient burn of the fuel.
Typical fuel vapor systems are disclosed in a number of U.S. patents, including Davison, et al. U.S. Pat. No. 4,216,751; Champ, U.S. Pat. No. 3,072,113; Cunningham, et al. U.S. Pat. No. 2,285,905; Pantano, U.S. Pat. No. 2,882,882, and Long, U.S. Pat. No. 1,970,010. In each of these systems raw liquid fuel is vaporized in a vaporization chamber heated by exhaust gases discharged from the engine. The fuel vapor is subsequently mixed with most, if not all, of the air needed for combustion and delivered to the engine.
These systems have a number of disadvantages. With the possible exception of Long, each of the above systems delivers liquid fuel at or close to ambient temperature to the vaporization chamber. Since the temperature of the fuel must be increased substantially to its vaporization temperature before vaporization will occur, a considerable amount of heat must be supplied. As a result, a significant percentage of the fuel delivered to the vaporization chamber never vaporizes and must be either returned to the fuel tank or delivered to the engine in liquid form, thereby reducing the fuel efficiency of the system. The Long system apparently preheats the liquid fuel in a primary heater pipe, but the amount of heat supplied appears to be minimal and not enough to alleviate the problem.
In each of the above systems, it is also quite likely that a significant percentage of the fuel vapor cools and condenses as it travels from the vaporization chamber to the engine, since the fuel vapor is at a temperature not much above its condensation temperature and little is done to prevent heat loss, other than perhaps insulating the fuel vapor line or making the line as short as possible. Such condensation also reduces the fuel efficiency of the fuel vapor system. The condensation problem is compounded in Davison, Cunningham and Champ where a full supplement of air at or close to ambient temperature is mixed with the fuel vapor shortly before combustion, thereby cooling and condensing even more of the vapor. The Pantano and Long vapor systems introduce a small quantity of air into the vaporization chamber to mix with the fuel while it is being vaporized. However, this alleviates the problem to only a slight extent since most of the air is mixed with the fuel after it has been vaporized.
Additionally, the exhaust gases used by the above systems to vaporize the fuel dissipate rapidly after the engine is shut off, thereby causing the manifold and exhaust pipes carrying the exhaust gases to cool down rapidly. Thus, once the engine is shut off the above systems are incapable of supplying sufficient heat to vaporize the fuel and start the engine. As a result, a conventional liquid fuel system must be used to start and warm up the engine, even when the engine has been shut off for only a few minutes.
Finally, while vapor systems generally achieve a shorter, more complete and less wasteful burn of the fuel than liquid fuel systems, the fuel-air mixture combusted is inherently leaner. Thus, vapor systems, such as those discussed above, generally cannot generate as much power as liquid systems. The power output of the vapor system can be increased by supplementing the fuel vapor with liquid fuel, but then the overall fuel efficiency is reduced.
Accordingly, there is a need for a fuel vapor system which reduces the amount of unvaporized fuel in the vaporization chamber, reduces the amount of fuel vapor condensation, is capable of starting and running the engine without the help of a supplementary fuel system shortly after the engine is shut off, and produces sufficient vapor to satisfy the power requirements of the engine under most conditions in a fuel efficient manner.